Subject: [Sigtran] Client-server relation between two IPSPs

From: Ilie Glib <[email-masked]>
Date: Mon, 5 Dec 2005 16:19:23 +0100

Hello Folks,

could you, please, clarify how the client-server relation is
established between two IPSPs in all IP architecture (IPSP to IPSP).
Is there any difference between SUA and M3UA?

It seems most up-to-date description is for M3UA.

I've found tree alternative answers.

1) Are client / server roles provisioned per IPSP to IPSP relation? So
that one IPSP acts always as a client (for SCTP association
establishment and subsequent SUA signalling) while the other acts as a
server.
This follows the old M3UAbis "
- 1- IPSP Single Exchange (SE) model. One IPSP takes the role of the
- client and the other the role of the server. The behavior then is
- the same as the ASP-SGP scenario. An IPSP node following this
- model will be named as C-IPSP (client node) or S-IPSP (server
- node). The same node may act as a client with one peer IPSP and
- server with another peer IPSP. Also upon common agreement the role
- (client/server) of the IPSPs can be changed in different dialogs
- between two IPSPs."

2) Alternatively, are both IPSPs trying to establish SCTP association
and depending on what IPSP is first, it acts further as a client
according to the following quote from the RFC 3868
"5.2.1.  Establishment of SUA connectivity
...
The endpoint that establishes SCTP
   connectivity MUST also establish UA connectivity (see RFC 2960,
   section 5.2.1 for handling collisions) [2960].

   IP SEP A                                                  IP SEP B
   AS A                                                          AS B
   ASP-a1     ASP-a2                                 ASP-b2    ASP-b1

   [All ASPs are in the ASP-DOWN state]

   +-------------------------------ASP Up-------------------------->
   <-----------------------------ASP Up Ack------------------------+

                 +--------------ASP Up--------------->
                 <------------ASP Up Ack-------------+

   +---------------------------ACTIVE------------------------------->
   <-------------------------ACTIVE Ack-----------------------------+
"

3) new M3UAbis proposal
" + 1- IPSP Single Exchange (SE) model. Only a single exchange of ASPTM
+ or ASPSM messages is needed to change the IPSP state. This means
+ that a set of request from one end and acknowledge from the other
+ will be enough.
"

Items 2) and 3) mean that an IPSP has to have provisioned as many ASes
as there are remote SCCP/MTP entities, while item 1) reduces
considerably the amount of required configuration.
Item 3) improves network management and makes it possible to
decativate a signalling relation from both sides, which was not
possible before.

Any opinions?

Thank you in advance

Ilie

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---

From: "Tolga Asveren" <[email-masked]>
Date: Mon, 5 Dec 2005 10:20:28 -0500

Ilie,

There are currently two modes of operation defined for IPSP:

a)Single-Exchange mode (SE-IPSP)
This is a true peer-to-peer relationship. AS defines traffic at both ends. A
single ASPAC/ASPAC-ACK exchange is sufficient to open the path for traffic.
the path is used  bidirectionally.

b)Double-Exchange mode (DE-IPSP)
This, you can think as two SGP/ASP relationships coupled where each path is
used unidirectionally. For each path ASPAC/ASPAC-ACK exchange is performed.

I know the above is a very short description and the existing text in the
documents is not the best to prevent confusion, but just hold on a few days
more for a more complete answer.

    Thanks,
    Tolga

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]On
> Behalf Of Ilie Glib
> Sent: Monday, December 05, 2005 10:19 AM
> To: [email-masked]
> Subject: [Sigtran] Client-server relation between two IPSPs
>
>
> Hello Folks,
>